Investigating the performance of generator protection relays using a real-time simulator.

Abstract

Real-time simulators have been utilized to perform hardware-in-loop testing of protection relays and power system controllers for some years. However, hardware-in-loop testing of generator protection relays has until recently been limited by a lack of suitable dynamic models of synchronous generators in the real-time simulation environment. Historically, the Park transformation has been chosen as the mathematical approach for dynamic modelling of electrical machines in simulation programs, since it greatly simplifies the dynamic equations. However, generator internal winding faults could not be represented faithfully with the aforementioned modelling approach due to its mathematical limitations. Recently, a new real-time phase-domain, synchronous machine model has become available that allows representation of internal winding faults in the stator circuits of a synchronous machine as well as faults in the excitation systems feeding the field circuits of these machines. The development of this phase-domain synchronous machine model for real-time simulators opens up the scope for hardware-in-loop testing of generator protection relays since the performance of various generator protection elements can now be examined using the advanced features provided by the new machine model. This thesis presents a thorough, research-based analysis of the new phase-domain synchronous generator model in order to assess its suitability for testing modern generator protection schemes. The thesis reviews the theory of operation and settings calculations of the various elements present in a particular representative modern numerical generator protection relay and describes the development of a detailed, real-time digital simulation model of a multi-generator system suitable for studying the performance of the protection functions provided within this relay. As part of the development of this real-time model, the thesis presents a custom-developed real-time modelling approach for representing the load-dependent third-harmonic voltages present in the windings of a large synchronous generator which are needed in order to test certain types of stator-winding protection schemes. The thesis presents the results of detailed, closed-loop testing of the representative generator protection relay hardware and its settings using the developed models on a real-time digital simulator. The results demonstrate the correctness of the modelling and testing approach and show that using the phase-domain synchronous machine model, together with the supplementary models presented in the thesis, it is possible to evaluate the performance of various generator protective functions that could not otherwise have been analysed using conventional machine models and testing techniques.